----- On Apr 10, 2019, at 11:52 AM, schwidefsky [email protected] wrote:
> On Wed, 10 Apr 2019 11:50:39 -0400 (EDT) > Mathieu Desnoyers <[email protected]> wrote: > >> ----- On Apr 10, 2019, at 6:32 AM, schwidefsky [email protected] wrote: >> >> > On Tue, 9 Apr 2019 15:32:22 -0400 (EDT) >> > Mathieu Desnoyers <[email protected]> wrote: >> > >> >> Hi, >> >> >> >> We are about to include the code signature required prior to restartable >> >> sequences abort handlers into glibc, which will make this ABI choice >> >> final. >> >> We need architecture maintainer input on that signature value. >> >> >> >> That code signature is placed before each abort handler, so the kernel can >> >> validate that it is indeed jumping to an abort handler (and not some >> >> arbitrary attacker-chosen code). The signature is never executed. >> >> >> >> The current discussion thread on the glibc mailing list leads us towards >> >> using a trap with uncommon immediate operand, which simplifies integration >> >> with disassemblers, emulators, makes it easier to debug if the control >> >> flow gets redirected there by mistake, and is nicer for some >> >> architecture's >> >> speculative execution. >> >> >> >> We can have different signatures for each sub-architecture, as long as >> >> they >> >> don't have to co-exist within the same process. We can special-case with >> >> #ifdef for each sub-architecture and endianness if need be. If the >> >> architecture >> >> has instruction set extensions that can co-exist with the architecture >> >> instruction set within the same process, we need to take into account to >> >> which >> >> instruction the chosen signature value would map (and possibly decide if >> >> we >> >> need to extend rseq to support many signatures). >> >> >> >> Here is an example of rseq signature definition template: >> >> >> >> /* >> >> * TODO: document trap instruction objdump output on each sub-architecture >> >> * instruction sets, as well as instruction set extensions. >> >> */ >> >> #define RSEQ_SIG 0x######## >> >> >> >> Ideally we'd need a patch on top of the Linux kernel >> >> tools/testing/selftests/rseq/rseq-s390.h file that updates >> >> the signature value, so I can then pick it up for the glibc >> >> patchset. >> > >> > The trap4 instruction is a suitable one. The patch would look like this >> >> Great! I'm picking it up into my rseq tree if that's OK with you. > > Just added the patch to s390/linux:features for the next merge window as well. Sounds good! I'll carry it in my tree to have a comprehensive up-to-date list of rseq signatures for all architectures in a single tree. Worse-case the exact same change will be pulled from both architecture and rseq trees, which I don't think should be an issue, right ? Thanks, Mathieu > > -- > blue skies, > Martin. > > "Reality continues to ruin my life." - Calvin. -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
